The US has a bunch of land. A thought occurred involving the US's surplus military personnel spending their days, after waking up from their barracks in some state in the west, tending to a massive bamboo garden, including cultivation, pruning, and disposal into giant pits. The Wikipedia article for bamboo even mentions its use in carbon sequestration prominently. Having looked into this before, though, I turned up a few sources that said bamboo alone has no net negative effect on atmospheric carbon, and might actually increase it.